前言数据通信网（datacommunicationnetwork）是指提供数据通信业务的电信网。由某一部门建立并操作运行，为本部门提供数据传输的电信网称为专用数据通信网；由电信部门建立、经营，为公众提供数据传输业务的电信网称为公用数据通信网。邮电部门提供DDN数据电路和普通电话网的 Preface Data communications network (datacommunicationnetwork) refers to the telecommunications network to provide data communications services. A telecommunication network established and operated by a certain department to provide data transmission for its own department is called a private data communication network; and a telecommunication network established and operated by the telecommunication department to provide data transmission services to the public is called a public data communication network. Post and Telecommunications departments to provide DDN data circuits and ordinary telephone network